This invention relates generally to wind powered generators and more particularly to apparatus for controlling the pitch of blades associated with such generators.
A windmill utilizes an array of blades to convert wind energy into a rotational input to drive. In the case of a power generator, the rotational input drives an electrical current generator.
A challenge associated with harnessing wind energy is that wind speeds are inconsistent. In order to generate energy with minimal wind speeds, it is desirable to have a rather steep xe2x80x9cpitchxe2x80x9d to the blades which convert wind energy to rotational input. As wind speed picks up however it is preferable to have less of a pitch to avoid structural damage which might otherwise occur from rotational imbalance or too large a force input into the input shaft. Accordingly a governor assembly of some type is required in order to optimize windmill characteristics over a broad wind speed range.
Wind powered generating apparatus varies significantly in cost and complexity from large units operated by power generating companies to small units for residential use. In the case of large and sophisticated apparatus, control systems for such things as pitch may be quite complicated involving microprocessors and servo motors to optimize performance characteristics.
In the case of small generating units, cost considerations restrict the level of sophistication which may be built into any system for varying pitch of the windmill blades. Various devices exist for small wind driven generating apparatus which in general utilize centrifugal force associated with input shaft rotation and translate the centrifugal force to a rotational input on the blades through various assemblies utilizing gears, levers, pivots and other coupling arrangements.
A drawback to the prior arrangements is that they in general are mechanically complex which affects their reliability, expected life and maintenance requirements. Accordingly it is an object of the present invention to provide a simple pitch governing assembly for windmill blades which is mechanically simple, robust, reliable and inexpensive to manufacture.
A pitch governing mounting assembly is provided for securing a windmill blade to a windmill input shaft with a blade axis of the blade generally radially disposed relative to a rotational axis of the shaft. The governor reduces the pitch of the blade in response to an increase in rotational speed of the drive shaft. The assembly includes a first member connectable to the drive shaft and a second member connectable to an inner end of the blade. The second member is slidably received by the first member for relative axial movement therebetween along a governor axis generally aligned with the blade axis, between a first position and a second position. A rotator acts between the first member and the second member to cause rotation of the second member relative to the first member about the governor axis to reduce the pitch of the blade as the assembly moves from the first position to toward the second position. Biasing means are also provided which act between the first and second members to urge the assembly towards its first position.
The rotator may include a projection on one of the first and second members which registers with a slot or a groove on the other of the first and second members.
The second member may have a shaft which is received in a passage in the first member.
The assembly may further include a bearing disposed between the biasing means and at least one of the first and second members to reduce friction between the first and second members about the governor axis.
The biasing means may be a stack of Belleville washers. The second member may have a shaft which has a head at one end and is threaded at an opposite end for threadedly engaging the blade. The passage may be a bore extending through the first member for receiving the shaft. The rotator may be a pin extending from the shaft which engages a slot extending along the bore. The washers may extend about the shaft between the head and the first member. The bearing may be mounted between the biasing means and the first member. A respective thrust washer may be interspersed between the bearing and the biasing means and between the bearing and the first member.
The bore and the slot may be defined by a bushing mounted in the passage.
The slot may be hard faced.
The rotator may effect a total rotation of 18xc2x0 between the first position and the second position.
A windmill may also be provided which incorporates a pitch governing mounting assembly for securing the windmill blades thereto in accordance with the above.